The present invention relates to a crane which is suitable for example, for constructing a steel framework structure and a method for using the crane. More specifically, the present invention relates to a crane which has an arm having a plurality of pivotably jointed portions.
Conventionally, cranes are utilized in order to construct steel framework structures for reinforced concrete construction. If the construction is multistoried or semi-multistoried, tower-cranes are used having a revolving turntable which can be lifted according to the height of the construction by a climbing mechanism.
However, during construction of a steel framework structure using a tower-crane, steel bars etc. lifted by the crane swing to-and-fro, which makes it difficult to place the bars at proper positions and which necessitates the operator must be highly skilled. Furthermore, it is necessary to carry the construction elements such as bolts and nuts to and from another lift apparatus. These result in additional costs and a longer construction time.
Therefore, there has been a recent demand for multi-operative cranes which can be utilized not only for lifting object such as steel bars but also for assisting in the construction operation by enabling control of the position and direction of the objects being lifted. FIG. 16 shows one of these multi-operative cranes comprising a mast 1 erected on the ground, a revolving turntable 2 installed on the upper end of the mast 1 rotatable about a vertical axis, an arm 3 disposed on the revolving turntable 2 for upward and downward movement, and a clutching mechanism 4 attached to an end of the arm 3 for clutching construction elements such as steel bars F.
The arm 3 comprises four arm members 3a, 3b, 3c, and 3d, that are connected to each other to pivot about horizontal axes. These arm members 3a, 3b, 3c, and 3d are pivoted by hydraulic cylinders 5.
With such a multi-operative crane, not only can the mere lifting of steel bars or the like, be accomplished but also objects can be raised with control of their position and direction.
However, the multi-operative crane has the following problems of which it is an object of the present invention to solve:
Usually, for constructing steel framework structures, it is necessary to lift or move the crane depending on the situation of the construction site and the crane has to carry the raising object to the construction site. However, the conventional crane cannot be moved easily and consequently the range of reach of its arm 3 is limited. Therefore, the conventional crane is not always useful depending on the construction situation. Also, considerable cost and time for construction is needed since the components in the construction must be conveyed by lifting stages with a small lift.
Furthermore, another crane must be utilized for moving and assembling the crane. Especially, if another tower-crane is utilized for this, a climbing mechanism only used for the tower crane is needed, so that additional cost is involved.